SolarpunkHomes
Sign inCall us · +44 7510 081687
Solar
Solar · For traders

Should a small inverter go on a dedicated circuit, a ring final circuit or a fused spur?

Short answer

For fixed PV and battery inverters, a dedicated radial circuit from the consumer unit with a suitable, bidirectional-rated protective device is the normal design, and it keeps voltage drop near 1 percent. Connecting generation into an existing final circuit is restricted by BS 7671 551.7.2, reworded in A4, so check the regulation and manufacturer limits first.

Last checked 24 September 2026 · 1 source

In more detail

  • BS 7671 A4: 551.7.1 bidirectional protective device where energy flow is bidirectional; 551.7.2 split into 551.7.2.1 / 551.7.2.2.
  • MIS 3002 cl.5.6.8: AC cable sized to minimise voltage drop; ~1% domestic, up to 3% larger/long runs, measured cut-out to inverter terminals.
  • A3:2024 reg 530.3.201: consider bidirectional vs unidirectional devices (many RCBOs not marked bidirectional - IET).
  • Plug-in (<=800 VA) devices are the only generation intended for existing socket circuits (spec).

The facts, dated

  1. 01
    Recommended practicable AC voltage drop for domestic PV — 1 %

    standard · UK · checked 24 September 2026 · MCS

What we saw in the field

[QA review 2026-09-24] P-10 ADDS: field install used a switched FCU (13 A) after extending the ring; dedicated radial remains the normal design. P-11 UNVERIFIABLE against A4 text.

Sources

Last checked: 24 September 2026